In manufacturing semiconductor devices, a wafer is subjected to dicing to separate it into respective semiconductor chips (pellets). The separated chips are fixedly attached on substrates of a lead frame at the predetermined positions by means of a conductive adhesive agent (paste), with, for example, polyimide based or epoxy based synthetic resin used as the adhesive agent. An adhesive agent is applied to a substrate before a chip is mounted on the substrate. FIG. 2 shows an example of a die bonding apparatus used for application of an adhesive agent. In FIG. 2, a die bonding apparatus is generally represented by reference numeral 1, and a lead frame to which the adhesive agent is applied using the apparatus, is generally represented by reference numeral 2.
The die bonding apparatus 1 has a stationary bed 3 on which an x-direction movement table 4 is movably mounted in the x-direction. An x-direction drive motor 5 is mounted on the table 4 such that the x-direction movement table 4 is caused to move in the x-direction as an x-direction ball screw (not shown) is rotated by the motor 5. A y-direction movement table 6 is movably mounted in the y-direction on the x-direction movement table 4. A y direction drive motor 7 is mounted on the table 6 such that the y-direction movement table 6 is caused to move in the y-direction as a y-direction ball screw (not shown) which is perpendicular to the x-direction ball screw, is rotated by the motor 7. A z-direction movement guide 11 is fixedly mounted on the y-direction movement table 6. The z-direction movement guide 11 is generally formed in an inverted U-shape. The base of a syringe support 12 is supported by the guide 11 within its groove 11a and so as to be movable in the z-direction (up/down direction). A z-direction drive motor 13 is mounted on the guide 11 for movement of the syringe support 12 in the x-direction. A cam (not shown) of a predetermined shape, is fixedly coupled to the rotary shaft of the motor 13 so that the syringe support 12 moves up and down following the cam surface as the cam rotates. A syringe 15 is supported at the distal portion of the syringe support 12. The syringe 15 comprises a container 15b for accommodating therein the adhesive agent and a needle 15a from which the adhesive agent is discharged. In order to discharge the adhesive agent from the needle 15a, an air on/off type dispenser 16 is coupled to the container 15b.
FIG. 2A partially shows the detail of FIG. 2. As seen from FIG. 2A, the syringe 15 can be moved up or down within the support 12 by loosening a screw 12a so that the clearance between the substrate 2a and the tip of the needle 15a, with the support 12 moved to the lowest position, can be adjusted.
A lead frame 2, to which the adhesive agent is applied with the die bonding apparatus 1 constructed as above, has a plurality of substrates 2a juxtaposed in the x-direction as seen in FIG. 2. A semiconductor chip (not shown) prepared beforehand is mounted on and fixed to each substrate 2a. Bonding pads of a chip fixed on each substrate 2a are thereafter connected to lead wires (not shown) of the lead frame 2 by means of bonding wires.
Application of the adhesive agent to a substrate 2a by using the die bonding apparatus 1 shown in FIG. 2, is carried out in the following manner. With the syringe 15 set at a high position, position alignment in the x- and y-directions of the syringe 15 is made using the x- and y-direction drive motors 5 and 6. Upon completion of position alignment, the syringe 15 is moved downward using the z-direction drive motor 13 to discharge the adhesive agent from the needle 15a and apply it to the substrate 2a. Thereafter, the syringe 15 is moved upward using the z-direction drive motor 13. At the same time, the lead frame is moved in the x-direction with a transportation apparatus (not shown) so that a new substrate 2a next to the adhesive applied substrate 2a is positioned just below the needle 15a of the syringe 15. The above adhesive agent application operation is thus repeated. Semiconductor chips are sequentially mounted on and fixed to the upper surfaces of the substrates 2a applied with the adhesive agent, by means of a semiconductor feeding means (not shown) positioned behind the syringe 15 in the x-direction as seen in FIG. 2.
FIG. 3 is an up/down displacement chart illustrating the up/down movement of the needle 15a during one cycle of adhesive agent application. As shown in this chart, the displacement S of the needle 15a (or syringe 15) during one cycle of up/down movement corresponds to the rotation, by an angle .theta., of the cam fixed on the rotary shaft of the z-direction drive motor 13. In particular, rotation by an angle .theta..sub.a of the cam causes the needle 15a to move downward, and further rotation by an angle .theta..sub.c causes the needle 15a to hold the lowered position while the adhesive agent is applied, and following rotation by an angle .theta..sub.b causes the needle 15a to move upward. The up movement and down movement of the needle 15a are quickly carried out in accordance with one cycloidal curve.
In the above case, the upward movement of the needle 15a is quickly carried out upon rotation by an angle .theta..sub.b in accordance with one cycloidal curve. The various types of resins used as an adhesive agent essentially have high viscosity characteristics. Therefore, if the needle 15a is raised quickly as described above after it has discharged the adhesive agent onto the substrate 2a, stringing of the adhesive agent A will occur as shown in FIG. 4. The amount of stringing of the adhesive agent is dependent on what material is used as adhesive agent, i.e., on the viscosity and other characteristics of the particular adhesive agent. If the adhesive agent having a large amount of stringing is used, the strung adhesive agent may fall down onto an area other than a predetermined area for application of the adhesive agent.